Answer:
Gupta Empire - People throughout the former empire continued to read Sanskrit literature.
The Gupta Empire adopted Sanskrit as its official court language and as a result most literature including poems and plays were written in Sanskrit. It's use became so widespread that after the decline of the empire in the 6th century AD, Sanskrit continued to be actively used by the people in the area. Even now Sanskrit is recognised as a minority language by the Indian government.
Han Dynasty - The population significantly declined after constant war between three kingdoms.
The Han dynasty of China is generally praised for ushering in a golden age of Chinese reformation that led to expansion and prosperity. The emperors were generally said to be benevolent and the Chinese fared relatively better during this time. When the empire fell however, war engulfed the nation as powerful warlords aimed to occupy the power vacuum left by the Han. 3 mighty kingdoms emerged known as the Wei, Shu, and Wu and they fought a series of wars that devastated China and reduced the population from 50 to 16 million.
Roman Empire - Christianity provided people with a sense of order and purpose amidst the chaos.
Under Constantine the Great, Christianity was made the official religion of the Roman Empire and many were converted. After the Western Roman Empire fell, the barbarian kingdoms that eventually took over parts of the now defunct empire converted to Christianity with Clovis I, king of the Franks being amongst the first to do so. The Pope became a symbol of Authority whom the people looked up to and with his authority was able to provide the region with a sense of order.